1. Field of the Invention
The present invention relates to an electrostatic actuator for electrostatically driving a slider or a movable section and a method of driving the same, particularly, to an electrostatic actuator including movable sections that can be driven individually and a method of driving the same.
2. Description of the Related Art
An electrostatic actuator is small and lightweight and, thus, can be used for the focusing of a lens system mounted to an endoscope, a movable telephone such as a portable telephone or an apparatus such as various kinds of PDA (Personal Digital Assistant). Such being the situation, the electrostatic actuator attracts attentions in recent years.
FIG. 1 is an oblique view showing the construction of a conventional electrostatic actuator 100. As shown in the drawing, the electrostatic actuator 100 comprises a slider or movable section 101 and a stator 102. The movable section 101 is substantially in the form of a parallelepiped having a through-hole formed therein in a manner to extend in the longitudinal direction of the movable section 101, and the stator 102 is also substantially in the form of a parallelepiped having a through-hole formed therein in a manner to extend in the longitudinal direction of the stator 102. The movable section 101 is slidable into the through-hole of the stator 102 such that the movable section 101 is movable within the stator 102 in the longitudinal direction of the stator 102. Incidentally, a clearance of several microns is provided between the stator 102 and the movable section 101.
Also, a convex stripe electrodes 103A and 103B are formed by, for example, an etching in the movable section 101 so as to form a pair of electrode surfaces facing the inner surfaces of the stator 102. An optical system of lenses 104 having optical axes extending along the axis of the through-hole are fixed within the through-hole of the movable section 101. The movable section 101 is moved and the optical system of these lenses is also moved with the movable section 101 so as to adjust the focus of the optical system on a subject to be examined.
A wiring 105 for applying a driving signal to the movable section 101 is connected to the movable section 101. Glass plates 106A and 106B are mounted to those inner surfaces of the stator 102 which face the electrodes 103A and 103B, respectively, and first electrodes 107A of a first group GA and a second group GB and second electrodes 107B of a third group GC and a fourth group GD are formed on the glass plates 106A and 106B, respectively, by patterning a conductive material. The electrodes 107A of the first group GA and the second group GB are alternately arranged at the same pitch. Likewise, the electrodes 107B of the third group GC and the fourth group GD are also alternately arranged in the same pitch. Also, the electrodes 107A and the electrodes 107B are arranged deviant from each other by a half pitch.
The operation of the electrostatic actuator having the construction described above will now be described with reference to FIG. 2.
(1) In the first step, a voltage of +V [V] is applied to the first group GA of the electrode 107A. As a result, an electrostatic attracting force is generated between the electrode 107A of the first group GA and the electrode 103A. By this electrostatic attracting force, the movable section 101 begins to be moved toward the glass plate 106A of the stator 102, and the electrode 103A is attracted to the electrode 107A of the first group GA a predetermined time later.
(2) In the next step, a voltage of +V [V] is applied to the electrode 107B of the third group GC among the electrodes 107B, with the result that an electrostatic force is generated between the electrode 107B of the third group GC and the electrode 103B. By this electrostatic force, the movable section 101 begins to be moved toward the glass plate 106B of the stator 102. As a result, the electrode 103B is attracted to the electrode 107B of the third group GC a predetermined time later. The movable section 101 is moved to the right in FIG. 2 by a distance equal to half the arranging pitch of the electrode 106A or 106B, compared with the position described in item (1) above.
(3) Further, a voltage of +V [V] is applied to the second group GB of the electrode 107A, with the result that an electrostatic force is generated between the electrode 107A of the second group GB and the electrode 103A. By this electrostatic force, the movable section 101 begins to be moved again toward the glass plate 106A, and the electrode 103A is attracted to the electrode 107A of the second group GB a predetermined time later. The movable section 101 is moved to the right in FIG. 2 by a distance equal to the arranging pitch of the electrode 107A or 107B, compared with the position described in item (1) above.
(4) Still further, a voltage of +V [V] is applied to the fourth electrode GD of the electrode 107B, with the result that an electrostatic force is generated between the electrode 107B of the fourth group GD and the electrode 103B. By this electrostatic force, the movable section 101 begins to be moved again toward the glass substrate 106B, and the electrode 103B is attracted to the electrode 107B of the fourth group GD. The movable section 101 is moved to the left in FIG. 2 by a distance equal to 1.5 times as much as the arranging pitch of the electrode 107A or 107B, compared with the position described in item (1) above.
The steps of items (1) to (4) described above are repeated so as to move the movable section 101 to the right in FIG. 2 by a distance equal to half the arranging pitch of the electrodes every time each of the steps of items (2) to (4) is performed.
It should also be noted that, if the voltage is applied to the electrode in the order of items (4), (3), (2) and (1) described above, the movable section 101 can be moved to the right in FIG. 2 by a distance equal to half the arranging pitch of the electrodes every time each of the steps of items (3) to (1) is performed.
It is possible to move the lens 104 mounted to the movable section 101 by moving the movable section 101 by the steps of items (1) to (4) described above so as to adjust the focus of the lens 104 on the subject.
As described above, in the conventional electrostatic actuator, it is possible to move the movable section to a desired position so as to adjust the focus of the lens on the subject to be photographed. However, the conventional electrostatic actuator gives rise to the problem that it is impossible to realize the zooming function of magnifying or reducing the photographed image. The difficulty is based on the mechanism that the lens system is moved with a single movable section.
It should also be noted that, even if a plurality of movable sections are mounted to the conventional electrostatic actuator for magnifying or reducing the photographed image, it is necessary for the plural movable sections to be moved or fixed independently for magnifying or reducing the photographed image. In the electrostatic actuator of the conventional structure, however, it is impossible to operate the electrostatic actuator with the plural movable sections moved or fixed within the stator independently.
An object of the present invention is to provide an electrostatic actuator capable of independently operating movable sections for magnifying or reducing the photographed image.
According to a first aspect of the present invention, there is provided an electrostatic actuator, comprising:
first stator electrodes arranged in a predetermined direction and extending in a direction crossing the predetermined direction;
a second stator electrode arranged to face the first stator electrodes and extending in the predetermined direction;
a third stator electrode arranged to face the first stator electrodes and extending in the predetermined direction so as to be electrically isolated from the second stator electrode;
a first movable section provided with first and second movable section electrodes, arranged movable within a moving space in the predetermined direction, the moving space being defined between the first stator electrodes and the second stator electrode, the first movable section electrodes being mounted to the first movable section to face the first stator electrodes, and the second movable section electrode being mounted to the first movable section to face the second stator electrode; and
a second movable section provided with third and fourth movable section electrodes, arranged independently of the first movable section, the second movable section being movable within the moving space in the predetermined direction, the third movable section electrodes being mounted to the second movable section to face the first stator electrodes, and the fourth movable section electrode being mounted to the second movable section to face the third stator electrode.
According to a second aspect of the present invention, there is provided an electrostatic actuator comprising:
a stator including a hollow stator frame having a space extending in a predetermined direction, the stator frame having a first inner surface extending in parallel to the predetermined direction and a second inner surface facing the first inner surface, first stator electrodes arranged in the predetermined direction on the first inner surface and each of the stator electrode extending in a direction crossing the predetermined direction, and second and third stator electrodes electrically isolated each other, arranged on the second inner surface and extending in the predetermined direction;
a first movable section arranged in the space to be movable in the predetermined direction, the first movable section including first movable section electrodes facing the first stator electrodes, each of the first movable section electrodes extending in a direction crossing the predetermined direction, and a second movable section electrode extending in the predetermined direction to face the second stator electrode;
a second movable section arranged in the space to be movable in the predetermined direction, and including third movable section electrodes facing the first electrodes, each of the third movable section electrodes extending in a direction crossing the predetermined direction, and a fourth movable section electrode extending in the predetermined direction to face the third stator electrode, and
a driving circuit configured to supply a first driving signal to the first stator electrodes, to supply one of a second driving signal and a first holding voltage signal to the second stator electrode, and to supply one of a third driving signal and a second holding voltage signal to the third stator electrode so as to move both or one of the first and second movable sections in the predetermined direction.
According to a third aspect of the present invention, there is provided an imaging apparatus for forming an image of a subject on an image-forming surface, comprising:
first stator electrodes arranged in a predetermined direction and extending in a direction crossing the predetermined direction;
a second stator electrode arranged to face the first stator electrodes and extending in the predetermined direction;
a third stator electrode arranged to face the first stator electrodes and extending in the predetermined direction so as to be electrically isolated from the second stator electrode;
a first movable section having a first hollow space, provided with first and second movable section electrodes, arranged movable within a moving space in the predetermined direction, the moving space being defined between the first stator electrodes and the second stator electrode, the first movable section electrodes being mounted to the first movable section to face the first stator electrodes, and the second movable section electrode being mounted to the first movable section to face the second stator electrode; and
a second movable section having a second hollow space, provided with third and fourth movable section electrodes, arranged independently of the first movable section, the second movable section being movable within the moving space in the predetermined direction, the third movable section electrodes being mounted to the second movable section to face the first stator electrodes, and the fourth movable section electrode being mounted to the second movable section to face the third stator electrode.
a first optical lens system having a first optical axis arranged in the predetermined direction within the first hollow space;
a second optical system having a second optical axis arranged in the predetermined direction within the second hollow space, the image forming surface configured to face an image of a subject depending on the positions of the first and second lens systems relative to the image-forming surface; and
a driving circuit configured to supply a first driving signal to the first stator electrodes, to supply one of a second driving signal and a first holding voltage signal to the second stator electrode, and to supply one of a third driving signal and a second holding voltage signal to the third stator electrode so as to move both or one of the first and second movable sections in the predetermined direction.
According to a fourth aspect of the present invention, there is provided a method of driving an electrostatic actuator, the electrostatic actuator comprising:
first stator electrodes arranged in a predetermined direction and extending in a direction crossing the predetermined direction;
a second stator electrode arranged to face the first stator electrodes and extending in the predetermined direction;
a third stator electrode arranged to face the first stator electrodes and extending in the predetermined direction so as to be electrically isolated from the second stator electrode;
a first movable section provided with first and second movable section electrodes, arranged movable within a moving space in the predetermined direction, the moving space being defined between the first stator electrodes and the second stator electrode, the first movable section electrodes being mounted to the first movable section to face the first stator electrodes, and the second movable section electrode being mounted to the first movable section to face the second stator electrode; and
a second movable section provided with third and fourth movable section electrodes, arranged independently of the first movable section, the second movable section being movable within the moving space in the predetermined direction, the third movable section electrodes being mounted to the second movable section to face the first stator electrodes, and the fourth movable section electrode being mounted to the second movable section to face the third stator electrode; the method comprising:
supplying a first driving a driving signal to the first stator electrodes;
supplying one of a second driving voltage and a first holding voltage signal to the second stator electrode; and
supplying one of a third driving signal and a second holding voltage signal to the third stator electrode wherein both or one of the first and second movable sections move in the predetermined direction.